Stock paper often is wound into large heavy rolls prior to cutting, finishing or printing the paper for its end use. These large paper rolls may have an axial length of several feet and an initial diameter of several feet. The rolls of paper typically are wound around a core which may be mounted to an apparatus from which the paper may be unwound for subsequent finishing processes, cutting or printing. For example, the paper may be rapidly unrolled from these large heavy rolls and fed into machines where the paper may be processed to achieve the desired texture and/or finish, cut into smaller sizes, or printed.
Backstands are provided for rotatably mounting the large rolls of paper, and permitting the paper to be unwound rapidly for use in another machine. The large roll of paper may be rolled into proximity to the backstand. The core of the rolls may then be rotatably mounted to the backstand with the core of the roll being generally horizontal. The backstand then lifts the heavy roll to permit unwinding of the paper into the associated machine. The amount of elevational movement of the roll by the backstand depends on dimensional characteristics of the roll and the operational characteristics of the machine. In some instances the roll may be elevationally moved during the winding or unwinding process.
The backstand typically comprises a pair of bases each of which includes an inclined screw spindle. A carriage is threadably mounted to the inclined screw spindle. in particular, the carriage is provided with a bushing nut that is threadably mounted on the inclined screw spindle. Each carriage is further operative to rotatably mount one end of the core about which the large roll is wound. The two bases are disposed on opposite ends of the core and permit the large rolls of paper to be rotated thereon for unwinding the paper from the roll. Rotational movement of the screw spindle about its axis causes the carriage to translate along the inclined screw spindle. Thus, the rotation of the screw spindle causes the carriage to gradually move upwardly or downwardly along the inclined screw spindle to ensure that the large heavy roll of paper is in a proper elevational position relative to the associated machine.
As noted above, the rolls of paper used in the above described processes are extremely large and heavy and impose substantial stresses upon the apparatus to which they are mounted. It follows that the rotation of the screw spindle to elevate or lower the roll imposes substantial stresses on both the spindle and on the bushing nut. In particular, the bushing nuts often are manufactured from brass and are likely to wear. Excessive wear can cause the bushing nuts to strip and unintentionally slide gravitationally down the screw spindle. A failure of this type can severly injure any employee working nearby and can require a costly repair to the backstand assembly. Furthermore, the damage to the backstand results in substantial downtime for the complex machine into which the paper is being fed. The net result is that these easily damaged bushings can result in costly losses of efficiency and possible injuries to employees.
Safety devices have been developed for use with a variety of vertical screw elevators. For example, U.S. Pat. No. 4,279,329 which issued to Gehron on July 21, 1981 shows a vertical screw on which a lifting nut is disposed. The apparatus shown in U.S. Pat. No. 4,279,329 shows a safety nut integrally incorporated into the apparatus and disposed in spaced relationship below the lifting nut. In the normal operation of the apparatus, the safety nut carries none of the lifting forces. However, after the threads of the lifting nut are worn, the safety nut will come into operation. The particular connection of the complex safety nut shown in U.S. Pat. No. 4,279,329 is such that upward movement of the lift carriage is prevented, but that a controlled downward movement is possible. This is enabled by the particular arrangement of the safety nut with a lock nut and a spring element disposed therebetween.
Another prior art apparatus which incorporates a safety device into a vertical lift elevator is shown in U.S. Pat. No. 3,687,234 which issued to Gendreau on Aug. 29, 1972. This prior art reference is directed to an apparatus for lifting automobiles. The apparatus includes rotatable screws on which carrier nuts are mounted. The carrier nuts in turn are connected to the horizontal arms which are operative to lift the vehicle. As a result of this construction, the rotation of the threaded columns will cause the carrier nuts and the arms connected thereto to move upwardly or downwardly. A safety nut is mounted below the carrier nut, but peforms no weight-bearing function during normal operations. However, if the carrier nut fails, the load that had been supported by the carrier nut will be transmitted to the safety nut via a sleeve disposed therebetween. The safety nut device shown in U.S. Pat. No. 3,687,234, as in the previously described prior art, is integrally incorporated into a complex lift apparatus.
U.S. Pat. No. 3,309,060 shows a fork lift where the lifing action is achieved by movement of a bearing nut along a vertical threaded column. The apparatus further includes a safety nut disposed below the bearing nut. As in the previously described reference, the safety nut normally does not perform a load-bearing function. However, as with the previously described references, the safety nut will peform a load-bearing function relative to the vertical threaded column upon a failure of the bearing nut. Once again, however, the safety nut is intregrally built into the complex apparatus.
In view of the above, it is an object of the subject invention to provide a safety nut apparatus that can be retrofitted onto an existing machine.
It is a further object of the subject invention to provide a safety nut apparatus that can be incorporated into a backstand for moving large rolls of paper.
Still a further object of the subject invention is to provide a safety nut apparatus for use with an inclined screw spindle for moving large rolls of paper relative to a paper processing machine.